The use of mobile communications networks has increased over the last decade. Operators of the mobile communications networks have increased the number of base stations and/or base transceiver stations (BTS) in order to meet an increased demand for service by users of the mobile communications networks. The operators of the mobile communications networks wish to reduce the costs associated with installing and operating the base stations. This wish for cost reduction has led network operators and manufacturers of network infrastructure to come up with new concepts for the network architecture. One of these architectures is known as “BTS Hoteling”. In the BTS Hoteling approach, the remote radio head is moved further from the remainder of the BTS, to enable the remainder of the BTS to be co-located with similar parts of other BTSs (for an entire city, for example) to form a BTS hotel. The BTS Hoteling approach involves all of the baseband/control/transport parts of a number of base stations being housed at the same location (e.g. for ease of maintenance and to save housing costs). The BTS hotel and the remote radio head(s) are connected by means of dedicated fibre-optic links, for example, from the BTS baseband sections to their respective remote radio heads
Most modern mobile communication networks are designed as cellular networks. The service area of the mobile communications network is divided into cells and usually each cell is covered by one base station. In the context of this disclosure, a “channel” refers to a private communications channel from a user to the person or service he/she wishes to connect to; a channel does not imply a single radio frequency is used for each communications channel. In the case of CDMA, for example, the “channel” referred to is in fact a combinations of a radio frequency carrier frequency and a user-specific spreading code or a spreading code plus a user-specific offset. A mobile station that is moving away from the area covered by one cell and is entering the area covered by another cell may experience a reduction or loss of connectivity when the phone gets outside the range of the first cell. In this situation the mobile communications network usually performs a handover which refers to the process of transferring an ongoing call or data session from one channel (base station) connected to a core network of the mobile communications network to another channel (base station). Other reasons why a handover might be conducted are that the capacity for connecting new calls of a given cell is used up and an existing or new call from a phone, which is located in an area overlapped by another cell, is transferred to that cell in order to free-up some capacity in the first cell for other users, who can only be connected to that cell; in non-CDMA networks then the channel used by the phone becomes interfered by another phone using the same channel in a different cell, the call is transferred to a different channel in the same cell or to a different channel in another cell in order to avoid the interference. A basic form of handover is called inter-cell handover. During an inter-cell handover a phone call in progress is redirected from its current cell and its used channel in the current cell to a new cell and a new channel. In terrestrial networks the source and the target cells may be served from two different cell sites or from one and the same cell site. In the latter case, the two cells are usually referred to as “sectors” on that cell site. The purpose of inter-cell handover is to maintain the call as the subscriber is moving out of the area covered by the source cell and entering the area of the target cell.
A special case is possible, in which the source and the target are one and the same cell or sector and only the used channel is changed during the handover. Such a handover, in which the cell is not changed, is called an “intra-cell handover”. The purpose the of intra-cell handover is to change one channel, which may be interfering or fading, with a new, clearer, or less fading channel.
Currently, the handover from one BTS site to another is achieved by re-routing of the user data from one cell site to another, using some form of switching centre. This necessitates a large amount of data flowing to and from the site, making its operational expenditure (OPEX) high. Typically, there are only three or four mobile switching centres per operator and country. The nearest mobile switching centre may be 10's or 100's of kilometres from the BTS sites themselves, although the distance between the BTS sites is usually in the range of 100's of meters, only. The handover also involves the transfer of the base band (user) data from one cell site to another, with the carrier frequency used and, where relevant, the spreading code used.